The invention is directed to a method and device for reducing the foaming tendencies of reactions between liquids and solids which are accompanied by the evolution of gas.
Whenever gases are evolved from liquids, there is a tendency for the system to form a foam the stability of which varies highly from system to system. Among the variables which affect foam stability are viscosity, temperature, turbulence and surface tension. By and large, the formation of foams at best serves no useful purpose and is frequently a serious operating problem in that large amounts of non-gaseous product or reactant are lost to the evolving gases and frequently must be separated by further unit operations. In some instances, the necessity to reduce foaming may require operation at unnecessarily high temperatures.
Many mechanical means have been devised and used to "knock out" or "break" foams, e.g. demisters, baffles, sprays and impingement caps. However, these approaches may in some instances not be very effective for mechanically stable foams such as those produced during the reaction of viscous liquids at high temperatures accompanied by the evolution of substantial quantities of gas. A quite interesting example of a commercial process in which the problem has existed for many years is the manufacture of sodium bisulfate.
Sodium bisulfate is manufactured by a process involving the high temperature reaction of sulfuric acid with salt as follows: EQU NaCl+H.sub.2 SO.sub.4 .sup.Heat NaHSO.sub.4 +HCl(gas).
The reaction is carried out on a commercial scale in large reactors in the molten phase. It has been found that, depending on the reactor temperature, the amount of foam build-up in the reactor varies and that excessive foaming interferes with the process. This gives rise to considerable impetus to reduce foaming in order that lower reaction temperatures and concomitantly lower energy costs can be realized.